This invention relates to the process for preparing a mercaptan by the reaction of an ethylenically unsaturated compound with an excess of hydrogen sulfide in the presence of ultraviolet light (UV) as a catalyst. The method of this invention involves the inclusion of a certain class of acetophenone derivatives with the reactants to provide much faster reaction rates.
Organic sulfur compounds, e.g., mercaptans, are of considerable commercial importance. A convenient and potentially economical process for the production of mercaptans involves the addition of hydrogen sulfide to ethylenically unsaturated compounds in the presence of ultraviolet radiation. The reaction can be carried out in a batch or a continuous manner. Relatively high molar ratios of hydrogen sulfide to the unsaturated compound are required to obtain high yields of the desired mercaptan.
Ultraviolet light from a mercury arc is a very effective catalyst for the addition of hydrogen sulfide to a double bond (Reid, "Organic Chemistry of Bivalent Sulfur", Volume 1, pg. 21). In the presence of ultraviolet light, a relatively fast reaction is observed with the addition of hydrogen sulfide to propylene and butene-1. However, the rate of reaction of hydrogen sulfide with an olefin is known to decrease significantly with an increase in the molecular weight of the olefin.
This invention provides an improved method for the preparation of mercaptans by the reaction of hydrogen sulfide with ethylenically unsaturated compounds in the presence of ultraviolet radiation. Another object is to provide a method for the preparation of mercaptans characterized by a marked increase in the rate of reaction of hydrogen sulfide with the ethylenically unsaturated compound.
The reaction of this invention involves the "inverse" or non-Markownikoff reaction of hydrogen sulfide with an olefin. In the ionic (acid or base) catalyzed reaction, addition across the olefinic linkage takes place according to the Markownikoff rule, i.e., "normal" addition in which the sulfhydryl radical attaches to the unsaturated carbon atom having the lesser number of hydrogen atoms. In the reaction of this invention "inverse" or non-Markownikoff addition occurs in which the sulfhydryl radical attaches to the unsaturated carbon atom having the greater number of hydrogen atoms. This invention is especially useful for the preparation of primary mercaptans.
The reaction of an ethylenically unsaturated compound with hydrogen sulfide catalyzed by UV radiation is well known. For instance, see Organic Chemistry of Bivalent Sulfur Volume 1, pg. 21, E. Emmet Reid, Chemical Publishing Company, Inc., 212 Fifth Avenue, New York, N.Y., 1958.
The use of a wide range of acetophenone derivatives as photo initiators in various polymerization processes is also well known. In this regard, see U.S. Pat. No. 3,715,293 to Sander, et al, dated Feb. 6, 1973; U.S. Pat. No. 379,807 to Osburn, et al, dated Sept. 18, 1973; U.S. Pat. No. 3,050,452 to Louthan, dated Aug. 21, 1962; and U.S. Pat. No. 2,448,828 to Renfrow, dated Sept. 7, 1948.
The particular mercaptans prepared by the process of this invention have a wide range of commercial uses, which include the field of adhesives, agricultural chemicals, polymer chain stoppers, chain transfer agents, and cross linking additives, to name a few.